Depth and depth rate measuring system



Nov. 3, 1959 s. G. FISHER 2,910,867

DEPTH AND DEPTH RATE MEASURING SYSTEM Filed Sept. 29, 1955 5 Sheets-Sheet l Nov. 3, 1959 s. G. FISHER DEPTH AND DEPTH RATE MEASURING SYSTEM 5 Sheets-Shea? 2 Filed Sept. 29, 1955 R m my@ ed u S@ n m l l l I.|| l l l l I l IIL N6`l S- G. FISHER DEPTH AND DEPTH RATE MEASURING SYSTEM Nov. 3, 195.9

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Filed Sept. 29, 1955 5 lSheec's--Sheec 5 S. G. FISHER DEPTH AND DEPTH RATE MEASURING SYSTEM Nov. 3, 1959` Filed sept. 29, 1955 INVENTOR. sf TH a. FISHER BY 'M/ld@ M ATTORNEYS United vStates ,y Patent DEPTH AND DEPTH RATE MEASURING SYSTEM Seth G. Fisher, Sharon, Pa., assigner, by mesne assignments, to the United States of America as represented This invention relates to a measurement of the depth position of a body or a submarine when submerged in a iluid or the sea and the rate of change of the measured depth position when the body is moved to other depths. This application is related to my copendin'g application Serial No. 537,606, led September 29, 1955.

Accordingly, an object of .the present invention is to indicate accurately the depth position and the rate of change of the depth position of a submerged body in a uid over a wide range of depth.

Another object is to provide an apparatus capable of high` gain and stability with a very quick corrective response to any change in depth in the position of the body.

A further object of the invention is the Provision of a system capable of a high degree of accuracy or resolution having excellent repeatability in the measurement of depth position.

Another object is to provide direct numerical indication of a depth.

Still another object of the present invention is to provide indication of a wide range of depth rate measurement.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 shows a block diagram of the apparatus of the invention;

Figs. 2 through 5 show a schematic diagram of a preferred embodiment of the apparatus of the invention, wherein Fig. 2 is a schematic diagram of the sensing element and balance network;

Fig. 3 is a schematic diagram of the four-stage electronic amplifier;

Fig. 4 is a schematic diagram of the magnetic amplier, motor, generator, gear train, spiral potentiometer and depth indicator and depth rate indicator; and

Fig. 5 is a schematic diagram of the power supply and transformer.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts, there is shown schematically in Fig. 2 a sensing element and balance network. To solve the problem of measuring the pounds per square inch of static pressure of a tiuid at any particular depth and converting this measurement to an indication in feet at that particular depth, a pressure measuring device employing the strain gage principle connected as a Wheatstone bridge as a sensing element is used. For measuring the static pressure from 0 to 1000 feet of depth, a O to 500 p.s.i.g. SR-4 Baldwin ice 2v Fluid Pressure Cell 50 may be used. The voltage out` put of the cell is caused by the change in pressure of the fluid which varies the resistance of the cell which unbalances the Wheatstone bridge of the sensing element. The output of the Wheatstone bridge is passed through a balance network 60. This network -60 is designed for balancing the zero pressure condition of the cell both for resistance and reactance at a minimum voltage output by potentiometer, pot. 1, and variable capacitors C-1 and C-Z. In addition, the network is capable of adjusting the output of the pressure cell for a minimum (zero) pressure point by pot. 2 and for a maximum (1000 foot) pressure point by pot. 3. The potentiometers pot. 2 and pot. 3 are considered to be calibrating potentiometers. The controlling or spiral potentiometer 140 (Fig. 4) is connected within the balance network 60 and is a ten turn precision potentiometer with negligible capacitances. The function of the spiral potentiometer 140 is to balance the output of the pressure cell at any given pressure for a minimum voltage whose position or value becomes proportional to the depth of the body in the Huid. i

The external source of 115 volts, 400 cycles, threephase voltage is applied to the transformer 30, power supply 40, motor 90, generator100, and rate indicator 105. The transformer 30 supplies filament voltage for the electronic amplier and 8 volts R.M.S., 400 cycle voltage to the pressure cell 50. The pressure of the fluid in which the body carrying the present apparatus is submerged, causes the resistance of the pressure cell 50 to change which gives a particular output or voltage per foot of depth. The output ofthe cell 50 is 7.12imicro'- voltsper foot of depth.v In salt water each additional foot of depth increases the static pressure 0.4465 p.s.i.

At a particular depth if the pressure cell 50 is measuring a different depth pressure than is indicated by the ten turn or spiral potentiometer 140, there exists a voltage across the output of the network greater than the balanced minimum voltage for that particular depth. This increased or error voltage is amplied by the electronic amplier 70, and the magnetic amplifier 80. The speed and direction in rotation of a servo motor is controlled by the output of the magnetic amplifier 80. Servo motor 90 may be of the type known to the Navy as Mk. l2, Md. 0. The motor is mechanically coupled through a gear train and antibacklash gear train 130 to drive the ten turn potentiometer 140 connected within the balance network so as to decrease this error voltage by making the potentiometer indicate thecorrect value for the particular depth. When the error voltage decreases to a minimum value, servo motor 90 stops and the ten turn potentiometer 140 has been driven to a new position proportional to the static pressure applied to the pressure cell.

By means of adjustil g potentiometers, pot. 2 and pot. 3, in the balance network, the spiral ten turn potentiometer 140 is adjusted to have a range of a hundred feet of depth error per revolution. By gearing the ten turn potentiometer rotation upwards to the ratio of ten to one and adding a digit counter capable of indicating tenths of a revolution, a numerical indication of depth in one foot increments is obtained and the counter will thus read directly in feet of depth. With the addition of ten subdivisions between successive numbers, the counter will then indicate tenths of foot of depth.

Since the above apparatus for measuring the depth of a position of a body in a uid, has a fast responding hi'g'lily stabilized lservosystem, the transient response to the 'error voltage has `a short `time vconstant and is well damped. This means that as the static depth pressure changes the system will follow the depth measurement at rates up to the maximum speed of the servo motor with very low error between the indicated depth and the actual depth pressure. As a consequence, the speed of the servo motor is proportional to the rate of change of depth position. Thereis mounted a 400 cycle -A.generator 100 .as .an ,integral part -of theservomotor 9.0. The output of this generator is proportional to the speed of the motor, therefore, `the voltage of this generator becomes a kmeasure of rate .of change of depth position. The polarity .of the generated voltage indicates the direction of .the ,rate lof change `of .depth position.

l Since AC. voltrneters are not polarity sensitive, a voltage of the Iproper magnitude and phase is added in series -with the generator output and this combined voltage .is then metered to indicate the rate-.of change of depth fposition. The alternating current voltmeter will kthen he Aused 'as a depth rate indicator 105. The -rneter will indicate `zero Arate-of Acha-nge of depth position at mid-scale and will-indicate `an increasefor rates .ofchange of depth position producing generated voltages in phase withthe xed voltage 'and will :indicate .sa decrease for rates Aof change of depth position producing generated voltages 180 degrees out of Vphase with the :fixed voltage of 115 volts, -400 cycles.

An indication of kdual range on the voltrneter vor Vrate indicator 105 is obtained by using the meter 105 `with two diierent voltage ranges and two fixed voltages of diiferent magnitudes as `shown by pot. 5 and pot. 6 in Fig. 4,. Thus, the rate indicator `can .be adjusted to indicate depth rates from Vto 6.5 feet per second climb or di-ve and from 0 to ,2.5 feet per second climb or dive withalinearity :and accuracy of 15% of full scale. The maximum .value .ofdepth rate .can be either increased or decreased by lchanging the gear ratio between lthe servo 4motor and the counter .for `the'depth indication. Remote indication can "be .accomplished iby :adding more voltmeters 106 .in parallel in a similar manner as yshown in Fig. 1.

The measuring system may be a completely contained unit housed in `a volume of approximately 114 inches by l2 inches by 7 .inches and weighing approximately 20 pounds. All voltages may `be obtained within the .unit except for 115 volt, three-phase, 400 'cycle fpower. .Since ythe unit weighs little :and uses a strain gage type instead of a Bourdon type sensing element, -it is capable of with- -standing'shock This measuring system can be yadjusted to indicate depth from 10 .feet tto 1000 feet with -a linear-ity of :1 -0.5% of vfull scale and with a 'resolution `of one half foot.

The lrange could be increased or `decreased by selecting a pressure cell with a different range. The linear-ity Could be improved Zby using a hand calibrated scale to show-the position of the ten turn potentiometer 140 instead of the counter. The resolution could be impnoved by Stringing theresistance `of lthe ten rturn potentiometer over l5 or 20 turns. The system could be made to operate on 60'cycles `eithersingle-phase yor three-phase. Remote depth indication can be added by adding slave counters to the present depth counter. Thel preferred Way 4of adding remote indication as illustrated by Fig. 1 would be to gear down the ten turn potentiometer rotation by ratio of Al0 ,to 1 to a synchro generator 160 by an .antibacklash gear train 150. This synchro generator could then .drive -synchro .motors 170 .that in vturn would be geared upward V100 to l by an antibacklash gear train A4180 and kconnected to digit counter ,190 to show the measured depth.

In one :embodiment of the apparatus of the invention shown .merely by way `of example and rin nowise to be Considered l'as limiting the scope of the invention, the

be appropriate:

Resistors k Ohms Ohms R-l 10K R-lZ 100K R-2 9K R-13 33K R-4 200K R-14 12K R-S 33K R-15 390 R-6 18K R-16 510K R-7 100K R-17 220 R- K R-IS 220 R-9 33K R-19 510K R-10 10K R-20 560 R-ll v1.00K v Y l.'ltb es `'C'hnkes VTlt, 2, 3 5744 Ghms VT4 5703 L-l 3H225 L-Z 3H225 Polentometers Pot. 1 25K ohms initial balance. Pot. 2 500 ohms zero foot balance. Pot. 3 2.5K ohms "1000 foot balance. Pot. 4 500K ohms depth gain. Pot. `5 10K `ohms low rate calibration. Pot. y6 10K ohms high ratef'calibration. Spir lPot. 1K ohms.

Canalensers C-1 500 mrnfd. C-2 SOOmmfd."

C-3 Zmfd.

C-4 '2,mfd. C-S 40 mfd. '450`WVDC. C-6 40 mfd. 450 WVDC. C-7 l mfd. C-9 .01 mfd. C-10 .l mfd. l C-'11 .'01 mfd. C-12 .0l mfd. C-13 .5 mfd.

It is therefore apparent in the light of the foregoing description that the invention presents a zqnick, stable and accurate solution for measuring a depth position tand a rate of .change of :depth position.

4Obviously many modifications Vand variations of -the present invention .are possible in the light yof the above teachings. It is therefore :to be funderstood that within the scope of the appended :claims the invention maybe practiced otherwise than as specifically described.

What is claimed is:

l. An underwater ydepth and depth-changerate measuring system comprising, in :combination: a :pressureresponsive cell of strain-gage Wheatstone bridge ktype adapted to be unbalanced in accordance with'the underwater depths and correspondingly with Ithe pressures 'to which said lcell is subjected; means Vfor :energizing said strain-gage bridge from a Voltage source, Isa-'id bridge 'then normally providing a voltage-difference output corresponding to the bridge imbalance; said strain-'gage bridge having a lirst pair of diagonally opposite junctions -to which energizing voltage from said .source is applied, and a second pair of diagonally opposite junctions at which said voltage-difference output appears; potentiometer means having a resistor element in `circuit between said second pair of junctions, and having a contact yarm positionable to connect Ian 'intermediate point 'of said resistor element to one of said rst pair of junctions, V"to effect a rebalanced condition of the resultantbrid'ge cir cuit at any measurement depth; servo means including a servo motor responsive to said voltage-difierence ouh put to drive and displace said .potentiometer arm I`to a resultant bridge balancing position at which the voltage difference output becomes substantially zero; first means responsive to the displacement experienced by said potentiometer arm to provide an indication of underwater depth; and second means responsive to the displacementrate experienced by said potentiometer `arm to provide an indication of the depthechange-rate to which said presstue cell is subjected.

2. An underwater depth and depth-change-rate measuring system comprising, in combination: a pressureresponsive cell of strain-gage Wheatstone bridge type adapted to be unbalanced in accordance with the underwater depths and correspondingly with the pressures to which said cell is subjected; means for energizing said strain-gage bridge from a voltage source, said bridge then normally providing a voltage-difference output corresponding to the bridge unbalance; said strain-gage bridge having a first pair of diagonally opposite junctions to which energizing voltage from said source is applied, and a second pair of diagonally opposite junctions at which said voltage-difference output appears; circuit means connected to said strain-gage bridge and modifying the balance condition thereof to yield resultant bridge balance at a preselected underwater depth and correspondingly tending to produce voltage-difference outputs at depths deviating from said preselected depth, said cir cuit means comprising series resistors connected between said second pair of junctions and having an intermediate point thereof connected to one of said rst pair of junctions; potentiometer means having a resistor element in 6 l circuit between said second pair of junctions, and having a contact arm positionable, in accordance with measurement depth relative to said preselected depth, to con nect an intermediate point of said resistor element to one of said first pair of junctions, to eifect a rebalanced condition of the resultant bridge circuit at said measurement depth; servo means including a servo motor responsive to said voltage-diiterence output to drive and displace said potentiometer arm to a balancing position at which the voltage-diierence output of the resultant bridge circuit becomes substantially zero; iirst means responsive to the displacement experienced by said potentiometer arm, relative to the bridge balancing position corresponding to said preselected depth, to provide an indication of underwater depth referenced to said preselected depth; and second means responsive to the displacement-rate experienced by said potentiometer arm to provide an indication of the depth-change-rate to which said pressure cell is subjected.

References Cited in the le of this patent UNITED STATES PATENTS 2,445,335 Philbrick July 20, 1948 2,530,022 Mershon Nov. 14, 1950 2,689,932 Hornfeck Sept. 21, 1954 2,704,936 Vine Mar. 29, 1955 2,718,783 Anastasia Sept. 27, 1955 

